Several communication techniques are available for enabling communication between a processor or a bus master and a plurality of serial devices coupled to the processor. Typically, the processor communicates with one or more serial devices sharing a common communication bus. In the event the processor needs to communicate information to a specific serial device, the processor must be able to distinguish the devices from each other. Various techniques are available to enable individual identification or selection of the serial devices.
For example, a separate select line may be used to enable each serial device. The serial devices are capable of responding or acting on information communicated when their respective select lines are asserted. One disadvantage of this technique is the imposed requirement for dedicated pins or exclusive signal lines on the processor to handle the device select signals. In particular, a separate select signal line is required for each serial device to be uniquely enabled.
Another technique uses jumpers, switches, or other hardware mechanisms associated with the serial devices to permit assignment of a unique identifier for each serial device. Each serial device only responds to commands with an accompanying identifier that matches that of the serial device as determined by the jumpers, switches or other hardware.
One disadvantage of this technique is that knowledge of other devices in the system is necessary to avoid duplicate device identifier assignments. Serial devices cannot be simply replaced or added into the system without first assigning a unique identifier. In addition, each device must have the ability to be configured for any one of a number of potential identifier assignments. For integrated circuit based serial devices additional packaging pins may be required to enable the serial device to support more than one potential identifier assignment.